Earlier, the 4½-month old cub’s daily public appearance was cut short after only 30 minutes and he was put on antibiotics.

“At the moment he is resting on his blanket and sleeping,” Schuele said, adding that despite his lethargy Knut did eat his regular meal in the morning.

Thousands of people line up daily to see the cub, and his button-eyed face has been a fixture for newspapers, television and the Internet.

Born at the zoo on Dec. 5, Knut was rejected by his mother and hand-raised by zookeepers. So potent is his appeal that zoo attendance has roughly doubled to 15,000 on average daily since his debut, officials said. He has his own blog and TV show and appeared on the cover of Vanity Fair.

Schuele did not know if Knut would be strong enough for public appearances in the next days.